We have continued our studies of chromatin structure in the neighborhood of expressed genes. The globin gene family in chicken erythroid cells serves as a model system in which it is possible to study the mechanisms associated with regulation of the individual members of the family during erythroid development. We have extended our studies of stage- specific erythroid expression in the alpha-globin gene family to the chicken embryonic alpha(pi)-globin gene, and shown that changes in the concentrations of three trans-acting factors that interact and that vary in concentration during development may account for much of the stage-specific expression. We have also extended studies of the structure and function of the general erythroid-specific factor GATA-1. We have continued investigation of the effects of chromatin structure on gene expression. We have investigated the structure and genesis of locus control regions (LCRs) in the human and chicken beta-globin loci. We have also identified a DNA sequence element far upstream in the chicken beta-globin locus that can serve as an insulator to block the action of an LCR/enhancer on a promoter. The insulating element functions both in human erythroid cell lines and in Drosophila, and may be part of a complex marking the boundary between chromatin domains. Work also continues on the effects of supercoiling on chromatin structure, and on the mechanism by which RNA polymerase transcribes through chromatin. We find that transcription through nucleosome cores involves an intramolecular transfer in which the core is displaced backward on the DNA without leaving the template.